As the valve of this type, there is known for instance the one disclosed in Japanese Utility Model Publication No. 36865/1982. In this valve 60, as shown in FIG. 1A to FIG. 1C, the stationary sleeve 64, whose inlet side has been closed, is fixed in the valve casing 63 having the inlet 61 and the outlet 62. Also, the movable sleeve 66 is fitted to this sleeve 64 slidably along the axial direction. In the peripheral wall of this sleeve 66 bridging from the axial middle portion to the inlet side, there are formed a plurality of tapered small holes 65 whose outer peripheral diameter is larger than the inner peripheral diameter, while the peripheral wall on the outlet side is solid. To this sleeve 66 there is attached the connecting rod 67 on the outside of the inlet side, and to this connecting rod 67 is further connected the tip of the working rod 68 which is provided slidably along the axial direction in the casing 63.
In the valve 60 as mentioned above, it takes place in the full-working state shown in FIG. 1A that when the sleve 66 is moved toward the right end position by the operation of the working rod 68, the fluid coming from the inlet 61 flows from the outside of the sleeve 66 through small holes 65 to the inside of the sleeve 66.
FIG. 1B indicates the non-working state where the sleeve 66 is transferred to the left side by the operation of the working rod 68, in which all the small holes 65 are closed by the outer periphery of the sleeve 64, and the small hole-free solid portion blocks the passage 69, thereby preventing the fluid from flowing out.
By moving the sleeve 66 between the position indicated in FIG. 1A and the position indicated in FIG. 1B, the number of opened small holes 65 is increased or decreased, and thus the flow rate is controlled.
When intending to remove the foreign substances having clogged some small holes 65, the sleeve 66 is moved toward the left end position indicated in FIG. 1C by the operation of the working rod 68. In this case, the fluid coming from the inlet 61 flows from the inside of the sleeve 66 through the small diameter portions of small holes 65 into the large diameter portions on the outside of the sleeve 66, whereby the foreign substances having clogged small holes 65 are pushed out thereof.
Even if a further large amount of fluid is hoped to be supplied on the downstream side urgently as the result of using for instance fire hydrants and the like provided in the downstream duct when the sleeve 66 is in the full-working state (FIG. 1A), the above mentioned valve can not comply with this demand, because the peripheral walls present between small holes 65 make a resistance against the fluid and consequently the resistance loss can not be lessened more than a fixed degree. In order to meet this demand, accordingly, it is necessary to move the sleeve 66 up to the middle position between the full-working position (FIG. 1B) and the washing position (FIG. 1C) and make the fluid flow between gaps formed between the front and rear outer peripheral surfaces of the sleeve 66 and the inner peripheral surface of the casing 63. In order to do so, however, it is required that the sleeve 66 should be first moved to the non-working position for stopping the flow of fluid and then moved up to said middle position, namely the sleeve 66 must be moved along a relatively long stroke. Accordingly, the aforesaid conventional valve has been observed to be disadvantageous in that it is impossible to change the flow rate from the non-working state to the high flow rate-flowing state while continuing the flow of fluid, and further it takes a relatively long period of time to attain said high flow rate, and in addition thereto when foreign substances have adhered to the outer periphery of the sleeve 66 they can not be removed with ease.
Still further, the aforesaid conventional valve has the following disadvantages. As the portion of the sleeve 66 having small holes 65 therein and the other solid portions are molded integrally, for instance when the relatively easy-to-damage portion is damaged the other portion, which is relatively difficult to damage and to which no damage has been caused yet, must be taken out together with said damaged portion for the repairing or exchanging purpose, and therefore materials are wasted and the expenses are increased.